This invention relates to a wide array thermal ink-jet print head for a printer.
Thermal ink-jet printers have become widely popular as inexpensive printing devices. An essential feature of a thermal ink-jet printer is a print head that is controlled to selectively eject tiny droplets of ink onto a printing surface, such as a piece of paper, to form desired images and characters.
The print head generally has an architecture plate with multiple tiny nozzles through which ink droplets are ejected. Adjacent to the nozzles are ink chambers, where ink is stored prior to ejection through the nozzles. Ink is delivered to the ink chambers through ink channels that are in fluid communication with an ink supply.
The print head usually is formed of a sandwich construction, having a substrate at its base. Attached to the substrate is a layer of circuit traces and a layer of the resistors. The resistors are overlaid with a protective, passivation layer. The architecture plate is bonded to the substrate and substantially covers the other layers.
The resistors are lined up beneath the chambers in the architecture plate. Electrical signal inputs to the resistors xe2x80x9cfirexe2x80x9d the resistors, heating the resistors and thereby a volume of ink within the adjacent ink chamber. The heating generates a vapor bubble in the ink to force an ink droplet out of the nozzle.
Usually, remote bus lines provide signal inputs from an external signal source to the resistors on the print head. Oftentimes, the signals are delivered through multiplexed circuitry on the substrate. The print head is generally connected to these bus lines by a thin flat electrical cable, such as a tape automated bond (xe2x80x9cTABxe2x80x9d) circuit. A TAB circuit generally has copper leads supported on a copper-coated tape. The tape is usually bonded onto the print heads with gold bump contacts. Conventional TAB circuit bonding cannot be done over live silicon circuitry without damaging the circuitry and requires use of an encapsulant to protect the leads from the ink, which adds a process step and decreases the robustness of the bond. Nevertheless, TAB circuit bonding is generally used because it is space-efficient, allowing the contact to be made in a tiny area.
In most ink-jet printers, the print head is mounted on an ink pen that is mounted to a carriage that traverses the printing surface to move the print head back and forth over the printing surface. Thus, the print head can be made relatively small in comparison to the width of the printing surface because the ink pen traverses the width of the printing surface. However, it takes the carriage a certain amount of time to traverse the paper, which slows down the speed of printing.
One way to increase the printing speed is to increase the number of nozzles on the print head, which necessitates an increase in the size of the print head. However, increasing the size of the print head requires a larger architecture plate, and a large architecture plate increases the likelihood of failure of the bonding of the interface between the architecture plate and the substrate. One reason for such failure is that the materials for the substrate and the architecture plate usually have considerably different coefficients of thermal expansion. Thus, the sandwich construction may bow or delaminate after assembly as the print head is heated and cooled during operation.
Sometimes, components within ink-jet printers are attached together by flip-chip processing. Flip-chip processing is the term used to describe the method of attaching two parts, such as a die and a substrate, by providing both parts with solderable pads, depositing a solder ball on the solderable pad on the substrate, then placing the solderable pad of the die on top of the solder ball, and heating and pressing the die and substrate to form a solder joint. Often, the solder ball is formed by depositing solder paste on the solderable pad on the substrate and heating the paste and pad to reflow the solder paste into a solder ball.
Oftentimes, after the two parts are attached by flip chip processing, an underfill made of liquid epoxy will be shot between the parts and allowed to wick therebetween, in a process separate from flip-chip processing. The underfill layer comprising the cured epoxy fills gaps between the parts and relieves some of the stress on the solder joint.
Page wide array printheads have been disclosed in U.S. Pat. No. 6,135,586, filed on behalf of Paul H. McClelland et al. on Oct. 31, 1995, titled xe2x80x9cLarge Area InkJet Printheadxe2x80x9d and U.S. Pat. No. 6,017,117, filed on behalf of Paul H. McClelland et al. on Oct. 31, 1995, titled xe2x80x9cPrinthead With Pump Driven Ink Circulationxe2x80x9d. These applications are assigned to the assignee of the present invention.
The invention generally includes a method of manufacturing a fluid ejection device by providing a substrate; attaching a plurality of resistors to a portion of the substrate for heating fluid; attaching a plurality of solderable interconnect pads to another portion of the substrate; soldering at least one chip onto the interconnect pads; and electrically connecting the resistors with the chip by attaching a layer having circuit traces that run from the interconnect pads to the resistors, whereby the chip is operable to control the resistors.